Change Neuroglancer state

[Andrei Mancu]

Hi,

we have been trying to get Neuroglancer to query only a subset of segment ids by querying the celltype in the segment_query search bar. The backend for this querying task is already set up.

For this, we added a callback, so we get the wanted celltype from the frontend with the viewer.shared_state.add_changed_callback(self.on_state_changed) (line 57) function. The  on_state_changed() function looks like this:

The set_state_segment_ids() creates a deep copy of the viewer state and sets the segment query of this state to a subset of the segment ids and returns it (new_state line 74). 

This approach results in a block, as the execution doesn't go past set_state (line 76)  method. It stops at _dispatch_changed_callbacks(), as add_changed_callback() (line 57) already acquired the lock.

Is this approach faulty? How could we set a new state for Neuroglancer Viewer with our preferred segmentation ids?

Thank you in advance!

Best regards,

Andrei Mancu

[Andrei Mancu]

As a follow-up:

The deadlock happens because the StateHandler also acquiring the lock for dispatching, but for receive_update() (sockjs_handler.py line 98), just before we want to use set_state. We tried to use the StateHandler to set the new state, but we did not find a way to access it.

Is there a way around this?

[Jeremy Maitin-Shepard]

To avoid deadlock, use the viewer.defer_callback method or run longer running computations on a separate thread.

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